Dimensions and geometric relationships of the human aortic valve as a function of pressure.

In a continuing effort to develop improved prosthetic heart valves, a redefinition of the anatomy of the human aortic valve as a function of stress was undertaken. Dimensions and geometric relationships of the human aortic valve as a function of intraaortic pressure between 0 and 120 mm Hg were obtained from a series of silicone rubber valve casts. The axial length of the valve region was found to vary negligibly with pressure, but significant variations in geometry and angular dimensions were seen. The leaflet attachment annulus forms an ellipse at the plane of intersection with the cylindrical surface passing from the left ventricular tract through the aorta. Deductions from stress considerations for the measured geometry indicate that the loaded leaflet is a section of a cylindrical surface. The equation for this developed surface was obtained, and a prosthetic design was determined using average values at 100 mm Hg. The leaflet is developable onto a plane with a cut required along part of the junction line between the initially cylindrical part and the plane coapting surfaces. Optimum valve shape mandates a base angle between the cylindrical leaflet and the center axis of 70° (a =20-22°, where a is the leaflet angle).